With performance enhancement in various electronic apparatuses, high densification of a semiconductor package substrate in particular is progressing, and reliability higher than it has been in the past is required for a photosensitive solder resist to be used in an outermost layer (hereinafter also referred to as permanent resist). Specifically, the need for crack resistance is increasing as the substrate becomes highly multi-layered and the size of a chip becomes large, and the crack resistance higher than it has been in the past is required at the time of a temperature cycle test especially.
Moreover, enhancement in fineness of a wiring pitch is also progressing with the high densification, and electrical insulation resistance is required even in a wiring pitch having, for example, a line/space of 8 μm/8 μm or less. As an acceleration test for electrical insulation resistance, a highly accelerated temperature and humidity stress test (HAST) is usually carried out. The highly accelerated temperature and humidity stress test is an extremely severe test in which insulation resistance is evaluated under the environment of 130° C. and 85% RH while the predetermined voltage is applied to a comb-shaped electrode of 8 μm/8 μm.
In the past, as a solder resist for use in a semiconductor package substrate, for example, a photosensitive resin composition using an alkaline developable acid-modified epoxy resin obtained by adding acrylic acid to a cresol novolak type epoxy resin and thereafter modified with an acid anhydride (see, for example, Patent Literature 1) or a photosensitive resin composition further comprising an elastomer for the purpose of improving resistance to a TCT (Temperature Cycle Test) (see, for example, Patent Literature 2) has been used.
Moreover, in recent years, a photosensitive resin composition comprising a silica filler for the purpose of improving reflow resistance (see, for example, Patent Literature 3) or a photosensitive resin composition using a photopolymerizable compound having a particular structure for the purpose of improving HAST resistance (see, for example, Patent Literature 4) has been used.